Various printing systems are known for recording (printing) character (text) or graphic (picture) images on a recording medium (receiver sheet) such as a paper or polymer sheet. These include:
(1) liquid ink printing systems as used in printing presses; PA1 (2) two-sheet pressure transfer inert ink printing systems as used in mechanical print head, stylus (pen) and like printers (pressure printers); PA1 (3) two-sheet heat transfer flowable dye printing systems as used in thermal print head, stylus (pen), laser and like printers (thermal printers); PA1 (4) two-sheet pressure transfer reactive dye printing systems as used in pressure printers; PA1 (5) one-sheet in situ pressure reactive dye printing systems as used in pressure printers; and PA1 (6) one-sheet in situ heat reactive dye printing systems as used in thermal printers, such as telephone transmission facsimile printers (FAX machines). PA1 (2) Two-sheet pressure transfer inert ink printing systems typically have an inert one-component colorant, formed of a pigment or dye containing liquid or paste, selectively transferred by printer pressure from a carrier medium (transfer sheet) such as a dye bearing ribbon (donor web) to a receiving medium (receiver sheet) to form images thereon. PA1 (3) Two-sheet heat transfer flowable dye printing systems typically have a heat sensitive one-component colorant, formed of a pigment or dye containing meltable, e.g., waxy, solid ink or a diffusible (sublimable) dye such as an anthraquinone dye, selectively transferred by thermal printer heat ( e.g., Joule heat) from a transfer sheet such as a donor web to a receiver sheet to form images thereon. PA1 (4) Two-sheet pressure transfer reactive dye printing systems typically have a pressure sensitive two-component particulate colorant, formed of a colorless or lightly (pale) colored dye precursor (leuco dye) such as crystal violet lactone (hereinafter CVL), i.e., 3,3-bis (4-dimethylamino phenyl)-6-dimethylamino phthalide, or malachite green lactone (hereinafter MGL), i.e., 3,3-bis (p-methylamino phenyl) phthalide, and a color developer such as bisphenol A, i.e., 4,4'-isopropylidene diphenol. Particles of one component are dispersed in a coating on a transfer sheet and particles of the other component are dispersed in a facing coating on a receiver sheet. At least one of the components is, or is contained in, a liquid, e.g., enclosed in pressure rupturable microcapsules, and is selectively transferred by printer pressure from its coating into reactive contact with the other component in the other coating to develop the dye precursor to color state and form images on the receiver sheet coating. PA1 (5) One-sheet in situ pressure reactive dye printing systems typically have a pressure sensitive two-component colorant, formed of particles of the dye precursor such as CVL, and particles of the color developer such as bisphenol A, dispersed in a coating on a receiver sheet, yet maintained out of reactive contact with each other. At least one of the components is, or is contained in, a liquid, e.g., enclosed in pressure rupturable microcapsules, and is selectively transferred by printer pressure into reactive contact with the other component to develop the dye precursor to color state and form, in situ, images in the receiver sheet coating. PA1 (6) One-sheet in situ heat reactive dye printing systems typically have a heat sensitive two-component colorant formed of particles of the dye precursor such as CVL, and particles of the color developer such as bisphenol A, dispersed in a coating on a receiver sheet for heat reactive contact. At least one of the components is, or is contained in, a meltable substance, e.g., bisphenol A, and is selectively melted and transferred at a given activation temperature by thermal printer heat ( e.g., Joule heat) into reactive contact with the other component, e.g., CVL, to develop the dye precursor to color state and form, in situ, images in the receiver sheet coating.
These printing systems and hybrid variations thereof are illustrated by the following prior art references [1] to [41].
References [1] to [12] concern identical two sided printing systems, and in one case a one sided transfer printing system.
[1] Grupe U.S. Pat. No. 2,333,172, issued Nov. 2, 1943; [2] Rockefeller, Jr. U.S. Pat. No. 3,329,088, issued Jul. 4, 1967; and [3] Dahlgren U.S. Pat. No. 4,208,963, issued Jun. 24, 1980, commonly disclose identical system liquid ink printing of both sides of a web.
Japanese Patent Document (English Abstract) [4] JP 4,555/90 to Imamura, dated Jan. 9, 1990, discloses a one sided two-sheet pressure transfer inert ink system in which printer pressure transfers an ink character from an ink ribbon to a roller which transfers it to the back side of a photosensitive sheet carrying an already exposed, but still undeveloped, image on its front side.
Japanese Patent Document (English Abstract) [5] JP 139,465/86 to Hamada, dated Jun. 26, 1986, discloses a pair of ink ribbons and associated print heads on opposed sides of a paper sheet for respective identical system printing on both sides of the sheet. It is unclear whether the ribbons are of the pressure transfer inert ink, or heat transfer flowable dye, type.
Japanese Patent Documents (English Abstracts) [6] JP 69,071/82 to Moriguchi, dated Apr. 27, 1982; [7] JP 202,863/86 to Watanabe, dated Sep. 8, 1986; and [8] JP 183,865/88 to Noaki, dated Jul. 19, 1988, commonly disclose a pair of ink ribbons and associated thermal print heads on opposed sides of a recording sheet for respective identical system heat transfer flowable dye printing on both sides of the sheet.
Japanese Patent Documents (English Abstracts) [9] JP 3,765/86 to Shimizu, dated Jan. 9, 1986 ([9] Shimizu JP '765); [10] JP 192,572/86 to Teraichi, dated Aug. 27, 1986 ([10] Teraichi JP '572); and [11] JP 113,571/87 to Teraichi, dated May 25, 1987 ([11] Teraichi JP '571), commonly disclose a pair of thermal heads on opposed sides of a paper sheet for respective identical system thermal printing on both sides of the sheet. The type of image recording performed is not indicated.
Japanese Patent Document (English Abstract) [12] JP 8,688/83 to Murakami, dated Jan. 18, 1983 ([12] Murakami JP '688), discloses a pair of thermal print heads on opposed sides of a paper sheet which is heat sensitive on both sides for respective identical system thermal printing on both such sides. The nature of the heat sensitive sides of the sheet is not indicated.
References [13] to [15] concern heat flowable dye transfer printing systems.
[13] Hotta et al. U.S. Pat. No. 4,541,830, issued Sep. 17, 1985 ([13] Hotta), discloses a two-sheet heat transfer flowable dye printing system having a transfer sheet bearing a sublimable dye which is flow transferred by a thermal head or laser beam to a receiver sheet to form images thereon. The dye may be one which sublimes below 100 degrees C. (column 5). The receiver sheet may be active clay coated paper.
[14] Long U.S. Pat. No. 4,804,977, issued Feb. 14, 1989 ([14] Long), which is assigned to the same assignee as the present invention, is similar to [13] Hotta. The receiver sheet may be a substrate of paper or of polyethylene terephthalate (hereinafter PET) film, with a receiving coating, e.g., of polycarbonate, which absorbs and retains the transferred dye images to give a bright hue and prevent subsequent dye wandering.
[15] Kawakami et al. U.S. Pat. No. 5,114,904, issued May 19, 1992, is to the same effect as [13] Hotta. The dye may be a sublimable or hot melt transfer dye. The receiver sheet may be a substrate of paper, polypropylene resin synthetic paper, e.g., of 150 micron (0.006 inch) thickness, or an inorganic sheet, with a receiving coating, e.g., of 5 micron (0.0002 inch) thickness, containing a dye permeating lubricant silicone resin, a high softening point and high glass transition point thermoplastic polymer resin, and a powdered inorganic filler.
References [16] to [20] concern pressure reactive dye transfer and in situ printing systems.
[16] Green et al. U.S. Pat. No. 2,730,456, issued Jan. 10, 1956 ([16] Green '456), discloses a two-sheet pressure transfer reactive dye printing system having a transfer sheet with a coating of microcapsules enclosing a liquid such as a water immiscible oil, carrying a dye precursor such as CVL or MGL, and a receiver sheet with a facing coating of a color developer such as an acid clay-like material. Printing pressure rupture of the microcapsules causes the liquid carrying the precursor dye to flow into reactive contact with the color developer to change the dye precursor to color state and form marks on the receiver sheet.
[17] Green et al. U.S. Pat. No. 2,730,457, issued Jan. 10, 1956, is to the same effect as [16] Green '456, but also discloses a one-sheet in situ pressure reactive dye printing system formed of a receiver sheet with a coating including both the microcapsules of the liquid containing the dye precursor such as CVL or MGL, and particles of the acid clay-like material. Microcapsule rupture causes the liquid carrying the dye precursor to contact and react with adjacent color developer particles in the same coating to form color marks. The disclosure describes the dye precursor as an electron donor compound having a double bond system, and the color developer as an electron acceptor which is acid relative thereto, the electron donor compound being converted to a more highly polar conjugated form giving it a distinctive color, upon reaction with the color developer.
[18] Sullivan U.S. Pat. No. 3,244,548, issued Apr. 5, 1966 ([18] Sullivan), is to the same effect as [16] Green '456, but uses a phenolic substance such as phenol, di- and tri-hydroxy phenols and 1- and 2-naphthol (columns 1 and 6-7) as color developer for the dye precursor, e.g., CVL or MGL (column 16). Many dye precursors are disclosed (columns 1, 5 and 12-24).
[19] Farnham et al. U.S. Pat. No. 3,244,550, issued Apr. 5, 1966 ([19] Farnham '550), is to the same effect as [18] Sullivan, disclosing many dye precursors (columns 18-30) including CVL (column 23) and MGL (column 22), plus biphenols (columns 3, 5 and 18-30) including bisphenol A (column 11) as color developers.
[20] Angleman U.S. Pat. No. 3,968,299, issued Jul. 6, 1976, discloses a two-sheet pressure transfer reactive dye printing system, with multiple component coatings on both sides of a pair of interchangeable transfer and receiver sheets, but operating like the system of [16] Green '456.
References [21] to [23] are mainly pertinent as concerning heat dependent, reversibly reactive dye development systems. [21] Farnham et al. U.S. Pat. No. 3,560,229, issued Feb. 2, 1971 ([21] Farnham '229), is to the same effect as [18] Sullivan, disclosing many dye precursors (columns 3-15) including CVL and MGL (column 7), and phenolic substances (columns 15-32) including bisphenol A (column 19) as color developers. It further discloses (column 37), inter alia, that if a dye precursor is dissolved in a certain type glycol ether, a permanent color forms on heating to about 150 degrees C., whereas if it is dissolved in a certain type phenol compound of low vapor pressure, which phenol compound is either liquid at room temperature or dissolved in certain organic solvents, a color forms at room temperature which disappears on heating to about 130 degrees C. and reversibly reappears on cooling back to room temperature.
[22] Igarashi U.S. Pat. No. 4,138,357, issued Feb. 6, 1979 ([22] Igarashi), discloses a one-sheet in situ heat reactive dye recording system formed of a receiver sheet with a coating of a reversibly color changing mixture of an electron donating color former such as CVL or MGL (column 2), i.e., a dye precursor, and a meltable special oxy benzoic acid ester (i.e., a hydroxy benzoate and thus a phenolic compound) having a melting point (mp) of about 50-200 degrees C. as electron accepting compound (columns 3-5), i.e., a color developer. On heating to melt the color developer, the mixture forms a color, and on cooling to crystallize the color developer, it returns to colorless state. In a given example (Example 1), a mixture of CVL and propyl p-oxy benzoate in a weight ratio of 1:100, coated on a paper sheet, changes from 0.09 optical density (colorless state) at normal temperature to 1.02 optical density (color state) when heated to 150 degrees C.
[23] Ito U.S. Pat. No. 4,940,689, issued Jul. 10, 1990, discloses a one-sheet in situ heat and electric current reactive recording cell. The cell is formed as a multilayer receiver sheet with an internal color forming layer of an oxidation-reduction dye such as CVL or MGL (column 3), and an electrolyte such as an aliphatic quaternary ammonium salt, in an insulating polymer medium which can dissolve the dye and electrolyte and which is liquid-solid transformable on heating and cooling. The dye reversibly changes from colorless to color state by applying heat to liquify the color forming layer and then electric current to induce an oxidation-reduction reaction of the dye.
References [24] to [33] concern heat reactive dye in situ printing systems.
[24] Baum U.S. Pat. No. 3,539,375, issued Nov. 10, 1970 ([24] Baum), discloses a one-sheet in situ heat reactive dye printing system formed of a receiver sheet with a heat activated image forming coating of a matrix of polyvinyl alcohol (hereinafter PVA) containing a mixture of CVL as dye precursor, and a solid phenol compound as acidic material, i.e., color developer, which liquifies and/or vaporizes at the usual thermographic temperatures of 150-200 degrees C., such as bisphenol A, mp 156 degrees C. (columns 3-4). Many phenol compounds and their melting points, ranging from a low of 86, to a high of 184, degrees C., are disclosed (columns 1-6). The coating has, by weight, 1-15% CVL, 45-94% phenol compound and 5.40% PVA. Heat activates the coating to develop an image by liquifying and/or vaporizing the phenol compound for reactive contact with the CVL. In a given example (Example I), a paper sheet is coated with a layer of 3% CVL and 67% bisphenol A (both of 1.3 micron particle size) in 30% PVA.
[25] Blose et al. U.S. Pat. No. 3,674,535, issued Jul. 4, 1972, is to the same effect as [24] Baum, with the image forming coating having a filler such as clay, a lubricant such as zinc stearate and a nontacky wax, e.g., of mp 140-143 degrees C., to inhibit sticking of the coating material to the thermal print head which liquifies and/or vaporizes the phenol compound such as bisphenol A for color developing the CVL.
[26] Hatano et al. U.S. Pat. No. 3,920,510, issued Nov. 18, 1975, is to the same effect as [24] Baum, with the dye precursor being a specific type fluoran compound (columns 2-18). In the use example (Example 18), a paper sheet is coated with, by weight (calculated), 3% 2-p-chloroanilino-3-methyl-6-dimethylamino fluoran as dye precursor and 67% bisphenol A as phenol compound, i.e., color developer, in 30% PVA as matrix.
[27] Oeda et al. U.S. Pat. No. 4,168,845, issued Sep. 25, 1979 ([27] Oeda), is to the same effect as [24] Baum, with the image forming coating having particles of the dye precursor such as CVL or MGL (column 2), and of the color developer such as bisphenol A (column 3), at least one of which are meltable particles providing a meltable color forming material. Oil absorption pigment particles of silicon dioxide, diatomaceous earth, etc., are added to absorb the melted color forming material to prevent its sticking to the thermal print head. Besides other additives, 10-40% of the solid content coating weight may be a binder such as PVA, gum arabic, starch, etc.
[28] Marginean U.S. Pat. No. 4,287,264, issued Sep. 1, 1981 ([28] Marginean '264), is to the same effect as [24] Baum. The receiver sheet has an image forming coating of PVA as carrier (binder, matrix) containing a mixture of a color forming amount of a finely divided homogeneous basic 3,3-bisaryl phthalane derivative such as CVL as dye precursor, and a color developing amount of a finely divided solid phenol derivative such as bisphenol A as acidic phenolic color developer, which at thermal printing temperature is at least partly fluidizable and capable of a color forming reaction with the dye precursor. An anti sticking amount of a functional filler is added to prevent the fluidized color developer from sticking to the thermal print head. A coating composition may have, by weight, 2-30% CVL, 16-36% bisphenol A, and 2-60% functional filler, e.g., zinc di-n-butyl dithiocarbamate (hereinafter butyl zimate), relative to the total solids in the composition. A given coating on a paper sheet (Example I) has, by weight, 3% CVL and 27% bisphenol A (both of 1-3 micron particle size), 30% PVA and 40% butyl zimate, and optionally talc.
[29] Marginean et al. U.S. Pat. No. 4,289,535, issued Sep. 15, 1981 ([29] Marginean '535), is cumulative to [28] Marginean '264. The PVA carrier of [28] Marginean '264 is replaced by a carrier composition of a substantially water soluble anionic polysaccharide gum such as gum arabic (about 16-50%) and a stability enhancing amount of sucrose benzoate (about 3-10%) as binder-carrier. This forms an image forming coating with the finely divided solid (1-3 micron particle size) chromogenous basic 3,3-bisaryl phthalane derivative such as 6-dimethylamino-3,3-bis (p-dimethylamino phenyl) phthalide, i.e., CVL (column 8), or 3,3-bis (p-dimethylamino phenyl) phthalide, i.e., MGL (column 6), as dye precursor, and finely divided solid (1-3 micron particle size) phenol derivative such as bisphenol A as color developer. The color developer is at least partially fluidizable at the printing temperature. Also includable are a functional filler (about 2-12%) such as zinc di-n-butyl dithiocarbamate, i.e. butyl zimate, and a pressure sensitivity eliminating agent such as a micronized polyolefin, or micronized modified (fluorinated) polyolefin, of 1,000 to 2,000 molecular weight (mol. wt.) and 240-700 degrees F. (116-371 degrees C.) mp to prevent pressure color development as occurs with pressure reactive dye printing systems. A preferred coating has, by weight, about 9-30% CVL, 16-36% bisphenol A, 16-50% gum arabic, 3-10% sucrose benzoate, 2-12% zinc zimate, and 2-12% high mol. wt. polyethylene or fluorinated polyethylene of about 240-700 degrees F. (116-371 degrees C.) mp. A given coating applied to a paper sheet (Example I) has, by weight, 11.10% CVL, 33.53% bisphenol A, 32.96% gum arabic, 6.07% sucrose benzoate, 8.17% butyl zimate, and 8.17% high mol. wt. polyethylene of above 500 degrees F. (260 degrees C.) mp.
[30] Yamato U.S. Pat. No. 4,399,188, issued Aug. 16, 1983 ([30] Yamato), discloses a one-sheet in situ heat reactive dye printing system formed of a receiver sheet with an image forming coating of a colorless or pale colored chromogenic fluoran type dye such as 3-diethylamino-6-methyl-7-anilino fluoran, and a specific type p-hydroxy benzoic acid ester (i.e., a first phenolic compound) of about 60-120 degrees C. mp as color developer, such as p-hydroxy benzoic acid ethyl ester or benzyl ester, plus a phenol substance (i.e., a second phenolic compound) of above 90 degrees C. mp, i.e., other than bisphenol A (Reference Example 1-a), such as 4,4'-butylene-bis (3-methyl-6-tertiary butyl phenol), which when used with said benzoic acid ester lowers the degree of yellowing on storage of the receiver sheet. A suitable formulation contains, by weight, per part of the fluoran type dye, 3-10 parts of said benzoic acid ester (first phenolic compound), 1-5 parts of the phenolic substance (second phenolic compound), 1-20 parts of an inorganic or organic filler such as kaolin, diatomaceous earth, talc, etc., plus 1-20%, per total solid content, of a binder such as PVA, starch, etc., and optional additives including a releasing agent such as a metal salt of a fatty acid, e.g., zinc stearate. Triphenylmethane phthalide type dyes such as CVL, rhodamine type dyes, spiropyran type dyes and leuco auramine type dyes are unsuitable in the formulation containing said benzoic acid ester as the color formed upon heating tends to discolor with the lapse of time. Thus, if CVL were used as dye precursor in this low melting point hydroxy benzoic acid ester containing coating, it would apparently function reversibly like the coating of [22] Igarashi which contemplates CVL and a similar hydroxy benzoic acid ester as phenolic compound, i.e., color developer.
[31] Wiklof et al. U.S. Pat. No. 4,604,635, issued Aug. 5, 1986 ([31] Wiklof), discloses a one-sheet in situ heat reactive dye printing system formed of a receiver sheet with an image forming inner coating of a leuco dye or metallic salt as dye precursor and an acidic material as color developer capable of coloring the leuco dye or metallic salt when heat is applied. A protective outer coating of a cured silicone resin on the inner coating contacts the thermal print head to prevent sticking thereto of the image forming coating ingredients. The silicone resin amount should not exceed 10 pounds per 3,000 sq. ft. of the receiver sheet (substrate) or the outer coating thickness will be too large to permit effective heating of the inner coating.
[32] Marginean et al. U.S. Pat. No. 4,675,705, issued Jun. 23, 1987 ([32] Marginean '705), is cumulative to [29] Marginean '535. The image forming coating has (by weight) a color forming amount (5-25%) of finely divided solid (1-3 micron particle size) colorless or pale colored chromogenic fluoran dye as dye precursor such as 6'-(cyclohexyl-methyl-amino) 3'-methyl-2'-(phenylamino)-spiro (isobenzo-fluoran-1-(3H),9,9(H) xanthene)-3-one. It also has a color developing amount (15-25%) of a finely divided solids combination of benzyl paraben, i.e., benzyl p-hydroxy benzoate, and a halogenated derivative of bisphenol A such as tetrabromo bisphenol A, in a 2-4:1 ratio of benzyl paraben to said halogenated derivative, as color developer, and which at the printing temperature is at least partially fluidizable and capable of a color forming reaction with the dye precursor. The fluoran dyes used as dye precursor (columns 1-2) differ from the fluoran dyes of [30] Yamato. The dye precursor and color developer are distributed in a carrier (binder) of substantially water soluble anionic polysaccharide gum (10-25%) such as gum arabic and a stability enhancing amount (1-10%) of sucrose benzoate. The composition may have additives such as an image stabilizing amount (5-10%) of an image stabilizer such as dimethyl terephthalate, and a filler such as calcium carbonate, titanium dioxide, aluminum hydrate, zinc stearate, waxes and zeolites. A given 1-3 micron particle size solids coating formulation applied to a paper sheet (Example) has, by weight, 7.36% 6'-(cyclohexyl-methyl-amino)-3'-methyl-2'-(phenylamino)-spiro (isobenzo-fluoran-1-(3H),9,9(H) xanthene)-3-one, 16.20% benzyl paraben, 5.42% tetrabromo bisphenol A, 20.20% gum arabic, 1.67% sucrose benzoate, 7.09% dimethyl terephthalate, 26.26% calcium carbonate, 0.92% titanium dioxide, 4.58% aluminum hydrate, 1.66% zinc stearate, 4.76% paraffin wax, and 3.50% zeolite.
[33] Yoshida et al. U.S. Pat. No. 5,061,677, issued Oct. 29, 1991, discloses a one sheet in situ heat reactive dye printing system formed of a receiver sheet protected against plasticizer and oil penetration. It includes a paper substrate of 40-100 micron (0.0016-0.004 inch) thickness, having on its front side an opaque inner layer, an image forming middle layer of a dye precursor and a color developer, and a protective outer layer for contacting the thermal print head and which has high smoothness for increased heat conduction efficiency. A plasticizer and oil penetration preventing back layer is disposed on the back side of the substrate as the opaque inner layer on its front side has an affinity for plasticizers and oils. The protective outer layer has a binder such as PVA, a filler such as calcium carbonate and a lubricant such as zinc stearate. The image forming middle layer has binders such as methyl cellulose and PVA, a dye precursor such as CVL, a color developer such as 4,4'-thiobis (2-methyl phenol), and optionally a thermally fusible substance such as a higher fatty acid amide, e.g., stearic amide, a wax, a higher fatty acid or ester, etc. The opaque inner layer has a binder such styrene-butadiene copolymer latex, with light scattering fine particles, up to 10 micron size, of a styrene-acryl copolymer that imparts opacity to the laminate. The back layer is formed of a binder such as PVA and a filler such as calcium carbonate.
References [34] to [41] concern hybrid or dual printing systems.
[34] Ueyama U.S. Pat. No. 4,688,057, issued Aug. 18, 1987 ([34] Ueyama), discloses a hybrid heat sensitive, simultaneous recording and transferring medium formed as a heat sensitive sheet of a substrate with a conventional heat sensitive color forming coating on its front side and a heat sensitive transferring ink coating on its back side. The sheet is overlaid on a plain paper receiver sheet with the ink coating contacting the paper sheet for printing letters thereon, in the manner of a donor web in contact with a paper sheet in a heat transfer flowable dye printing system. The color forming coating has a dye precursor such as CVL and a color developer such as bisphenol A in a binder such as PVA, starch, and the like, and optionally an auxiliary agent such as clay, talc and the like. The ink coating has three different waxes of mutually differing properties, an extender pigment such as calcium carbonate, clay, barium sulfate, talc and the like, and a coloring agent (ink), all in specified proportions, and optionally a softening agent such as an oil. Apparently, the thermal print head contacts the heat sensitive color forming coating and the heat sensitive ink coating contacts the paper sheet for simultaneously printing images in situ in the color forming coating and duplicate images on the paper sheet by ink transfer from the ink coating. Thus, the print head heat is conducted through the color forming coating and the substrate to transfer ink from the ink coating on the back side of the receiver sheet to the paper sheet.
[35] IBM Technical Disclosure Bulletin, Vol. 24, No. 1A, June 1981 to Kuntzleman et al., proposes coating the front side of a paper sheet with an energizable leuco dye combination, followed by the printing thereof by a write head, and then coating the back side of the sheet with such leuco dye combination, followed by the printing thereof by another write head. The type energizable leuco dye combination is not indicated. This proposal is akin to the initially noted printing systems of [9] Shimizu Jp '765, [10] Teraichi JP '572, [11] Teraichi JP '571 and [12] Murakami JP '688 (English Abstracts), but in view of [34] Ueyama, if a sheet with a heat reactive in situ image forming coating on its front side and also on its back side were printed by a thermal head on one side, the heat from the head would be conducted through the facing coating and the substrate, and also form duplicate images in the coating on the back side.
[36] Kubo et al. U.S. Pat. No. 4,500,896, issued Feb. 19, 1985 ([36] Kubo), discloses a hybrid heat sensitive two-sheet sequential heat transfer flowable dye printing system and heat transfer reactive dye printing system. It is formed of a two-layer transfer sheet and a one layer receiver sheet, to transfer in turn two different colors at two different temperatures from the transfer sheet to the receiver sheet. The transfer sheet is formed of a substrate having on its front side an inner layer of a meltable or sublimable solid ink of a first color and a meltable leuco compound discoloring agent that are melted or activated at a high temperature of 80-150 degrees C., overcoated with an outer layer of a colorless leuco compound of a second color such as CVL or MGL (column 5) as dye precursor that is melted or flow activated at a low temperature of 60-100 degrees C. The high temperature is at least 20 degrees C. higher than the low temperature. The receiver sheet is formed of a substrate having a developer layer of a leuco compound color developer such as bisphenol A, mp 156 degrees C. (column 6), in facing contact with the leuco compound outer layer of the transfer sheet. A thermal head acting on the back side of the transfer sheet operates at the low temperature to conduct heat through the transfer sheet substrate, inner layer and outer layer for melt transfer of the leuco compound from the outer layer to the leuco compound developer in the receiver sheet developer layer to form images of the second color thereon without activating the solid ink or discoloring agent in the inner layer of the transfer sheet. The thermal head then operates at the high temperature to conduct heat through the transfer sheet substrate, inner layer and outer layer for melt transfer of the ink from the inner layer to the receiver sheet developer layer to form images of the first color thereon, and at the same time for melt activation of the discoloring agent in the transfer sheet inner layer to prevent the leuco compound from forming the second color with the color developer in the receiver sheet developer layer.
The solid ink is formed of a fusible substance such as a wax, plus a colorant such as carbon black, crystal violet lactone (colored type), etc. (columns 3-4). The discoloring agent is an alcohol such as stearyl alcohol, propylene glycol, etc., capable when melted of preventing the leuco compound from forming a color with the color developer (columns 4-5). The color developer is a phenolic compound, an organic acid, or an ester or salt thereof, including those of indicated melting points ranging from a low of 50, to a high of 200, degrees C. (columns 6-7). The given layers may have a binder such as PVA, etc. (columns 5-6). The discoloring agent appears to function like the hydroxy benzoic acid esters of [22] Igarashi and [30] Yamato.
[37] Sato U.S. Pat. No. 4,940,993, issued Jul. 10, 1990 ([37] Sato); [38] Hakkaku et al. U.S. Pat. No. 4,962,386, issued Oct. 9, 1990 ([38] Hakkaku '386); and [39] Hakkaku U.S. Pat. No. 5,101,222, issued Mar. 31, 1992 ([39] Hakkaku '222), commonly disclose a hybrid one-sheet in situ heat reactive dye printing system formed of a transparent receiver sheet having transparent heat sensitive layers on its front and back sides for developing three color images by a thermal recording head. Yellow and magenta images are formed sequentially on the front side, and then the sheet is turned upside down to form a cyan image on its back side. The sheet is recorded by the head in three steps, in the first step also undergoing photo fixation of the yellow image by a light source. The sheet has a polyester film substrate, e.g., of PET, coated on its front side by an inner magenta layer that forms an image by high heat level head operation, and an outer light fixable yellow layer that forms an image by low heat level head operation, in turn being fixed by exposure to the light source to stabilize it against further development. The substrate is coated on its back side by a cyan layer that forms an image by high heat level head operation.
In the first step, the sheet moves past the head and light source to form and fix the outer layer yellow image on the front side. The low heat level of the head does not develop the inner magenta layer. In the second step, the sheet returns to the starting point and moves past the head to form the inner layer magenta image, the high heat level of the head not influencing the now stabilized outer yellow layer. Then, the sheet is turned upside down, returns to the starting point, and moves past the head to form the cyan image in the back side layer by operating the head at high heat level. While the outer yellow layer must be low heat reactive to avoid also developing the inner magenta layer, it is not stable at the low heat level of the head, and must be photo fixed before operating the head at the high heat level needed to develop the inner magenta layer.
[40] Washizu et al. U.S. Pat. No. 4,956,251, issued Sep. 11, 1990 ([40] Washizu), discloses a hybrid one-sheet in situ heat reactive dye printing system for sequentially color developing three color layers, i.e., yellow, magenta and cyan, akin to [37] Sato, [38] Hakkaku '386 and [39] Hakkaku '222. As exemplified (columns 20-25), the transparent receiver sheet has a PET film substrate coated on its front side with a high temperature heat reactive inner magenta layer of a magenta dye precursor (leuco dye) and a color developer, and a low temperature heat reactive and photo fixable outer yellow layer of a diazonium compound (diazo dye) and a diazo coupler. The substrate is coated on its back side with a high temperature heat reactive cyan layer of a cyan dye precursor (leuco dye) and a color developer. The outer yellow layer is developed by low temperature print head induced coupling reaction of the diazo dye and diazo coupler, followed by photo-fixing with particular wave length light. The inner magenta layer and the back side cyan layer are developed in sequence thereafter by high temperature print head heat induced reaction, but are not developed at the low temperature used to develop the outer yellow layer. The disclosure sets forth many diazo compounds (columns 6-9), diazo couplers (columns 9-10), leuco compounds including CVL and MGL, as dye precursors (column 5), color developers including phenol compounds, organic acids or metal salts thereof, e.g., of 50-250 degrees C. mp, such as in a weight ratio of 0.3-160 parts color developer per part dye precursor (column 11), layer forming binders such as PVA (columns 14-15), and fillers (columns 12-13).
[41] Kobayashi et al. U.S. Pat. No. 5,115,255, issued May 19, 1992 ([41] Kobayashi), discloses a thermal printer for use exchangeably with a two-sheet heat transfer flowable dye printing system or a one-sheet in situ heat reactive dye printing system. The two-sheet system of an ink bearing donor web as transfer sheet and plain paper as receiver sheet is physically replaced in the printer by the one-sheet system of a receiver sheet having a heat reactive dye color image layer (column 4), and the controls are reset (column 6), for one-sheet in situ reactive dye printing.
This most recent hybrid teaching, [41] Kobayashi, confirms the lack of availability of a two sided thermal printing system providing for both the receiving of a heat transfer printed image on one side of a sheet and the in situ printing of a different image on the other side of the same sheet.
As is clear from the foregoing, two differing systems of thermal printing currently exist for printing images on recording media such as paper sheets. One system is the one sheet in situ heat reactive thermal printing system, or simply the direct dye development thermal printing system, and the other system is the two-sheet heat transfer flowable dye thermal printing system, or simply the dye transfer thermal printing system.
In practice, in the direct dye development thermal printing system, a sheet of thermally reactive material as receiver sheet is conducted past a thermal print head to generate images directly therein by modulating (selectively energizing) the head, with respect to energizing time (pulse width) and heat level (Joule heat) per image pixel element, or simply pixel (e.g., of 0.003 inch pixel height and 0.003 inch pixel width, aspect ratio). In the dye transfer thermal printing system, the head is similarly modulated to transfer dye from a dye bearing carrier (dye transfer web, donor web) as transfer sheet to a dye receiving medium as receiver sheet, e.g., a paper sheet. These print heads are typically formed of a plurality of resistor elements such that when a given resistor element is energized it produces heat. In the direct thermal printing system, the heat causes direct formation of an in situ image in the sheet of thermally reactive material. In the dye transfer thermal printing system, the heat causes transfer of dye from the dye transfer web to the dye receiving sheet. In the printers of these systems, a rotating platen and other conveying means are normally used to move the thermally reactive sheet, or the dye receiving sheet together with the dye transfer web, past the head during printing. Associated motors are operated in such manner that the head modulation, platen rotation and operation of the other conveying means produce a series of pixel elements of correct aspect ratio on the given sheet.
More particularly, the direct thermal printing system uses a thermally reactive sheet having a coating of heat activated dye material particles that directly release or change pigmentation in situ on applying heat thereto, e.g., to change or develop directly in situ a leuco dye from colorless to color state. Coatings of this type are used commercially in facsimile systems (FAX machines). For instance, coated paper (FAX paper) is fed through a printing nip between a thermal print head and a platen, usually under slight compression, and the head is modulated as the FAX paper advances through the nip to form an image directly in situ by selective thermal activation of the dye material particles in the coating. These FAX papers typically, but not necessarily, are below 0.002 inch thickness (including the dye material coating) to permit intimate contact at low nip compression between the head and thermally activated dye material coating on the paper for efficient heat transfer to achieve direct color image development.
In the dye transfer thermal printing system, a dye transfer web bears the pigmentation, and the dye is selectively transferred from the web to a recording receiver sheet, using a thermal print head similar in construction to that of the direct thermal printing system, and an associated platen forming a printing nip with the head, typically under slight compression. The dye carried on the transfer web, which may be a wax based pigment or a heat diffusible (sublimable) dye, is selectively transferred to the receiver sheet to form the image by controlled modulation of the head.
In the wax based system, which is comparatively inexpensive and in which the print head operates at lower thermal levels for transfer of the wax based dye, plain (uncoated) paper of about 0.002 to 0.003 inch thickness is used. However, the transferred images are of comparatively poor clarity due to the uneven surface character of the uncoated paper on which the wax based dye is deposited. This is traceable to the surface discontinuities of plain paper. For maximum clarity and uniformity of the transferred images, the nip pressure must be kept uniform, and the receiver sheet recording surface must be uniformly smooth.
In the diffusible dye system, dye is deposited from a dye transfer web onto a special dye receiving coating disposed on a substantially thicker member as receiver sheet, e.g., coated paper, of about 0.005 to 0.009 inch thickness (including the coating). The density or darkness of the printed color dye is a function of the heat energy delivered from the individual resistor elements of the thermal head to the dye transfer web as transfer sheet. Thermal dye transfer printers of the diffusible dye system type offer the advantage of true "continuous tone" dye density transfer. This is achieved by selectively varying the energy applied to each resistor element of the head, to provide a variable dye density image pixel in the receiver sheet coating.
The dye diffusion process creates a more stable image but requires a substantially greater amount of heat to accomplish diffusion transfer than is needed for other types of thermal printing. The receiver sheet for the dye diffusion process may have several layers. Typically, a paper material substrate is coated on both sides with a layer of soft polymeric material such as polyethylene or polypropylene. The dye receiving side of the soft layer coated substrate is typically coated with a water based antistatic agent to permit solvent coating thereon of an outer dye receiving layer providing a dye receiving surface. The dye receiving layer is typically formed of high heat deflection material such as polycarbonate, solvent coated onto the soft layer on one side of the substrate, while the soft layer on the opposite side of the substrate remains exposed.
The multilayer composite formed with coatings on both sides of the substrate, is generally sufficient in thickness to withstand the higher level of heat required for thermal transfer of the diffusible dye from the web to the dye receiving layer on one side of the substrate. The soft layer on the opposite side of the substrate contributes to the stability of the composite and its ability to withstand the higher heat level needed for dye transfer.
It is desirable to provide a two sided thermal printing system formed of a sheet substrate having a front side coated with a heat transfer flowable dye receiving coating serving as a receiver sheet for thermal printer heat transferred first desired color images, transferred from an extraneous dye transfer source in a transfer printing step, and a back side coated with a heat sensitive, in situ heat reactive dye coating serving as a counterpart receiver sheet for thermal printer formed, in situ, second desired color images, unrelated to the transferred first color images, and formed by heat activation in an in situ printing step, such that the reactive dye coating is not activated to form in situ images under the attendant heat applied during the transfer printing step.
In particular, it is desirable to print on both sides of a sheet by dye transfer thermal printing on the front side thereof, e.g., using a multicolor transfer web having a successive series of different color dye areas for repeated thermal transfer printing of graphic color images on a same area on the front side, and by direct thermal printing on the opposing back side thereof, e.g., using a heat activated dye coating on the back side for printing text information thereon, without activating the dye coating on the back side during dye transfer printing on the front side.